Gas turbine engines generally comprise a compressor for compressing air flowing through the engine, a combustor in which fuel is mixed with the compressed air and ignited to form a high-energy gas stream, and a turbine which includes a first rotor for driving the compressor. In addition, many gas turbine engines are of the turbofan type in which a fan located forward of the compressor is driven by a second turbine rotor. The fan produces a flow stream which bypasses the compressor, combustor, and turbine to provide propulsion.
In assembling such gas turbine engines, the compressor with its many rotating blades and stationary vanes typically is assembled separately from the fan section. The rotating blades extend radially outwardly from disks which are attached to the first compressor rotor. The non-rotating vanes are interposed between successive blade stages and extend radially inwardly from a compressor casing.
The fan section includes a frame member to which the compressor casing may be fastened during assembly. In order to join the compressor and fan section together, it is known to include a radially directed flange on the forward end of the compressor casing in order to provide a surface for fastening to the fan frame. For example, axially directed bolts may extend through the frame and this flange to provide such fastening. Such flanges are effective for the purpose described, but add weight to the engine.
Non-rotating compressor stator vanes are attached at a root end of a vane to the compressor casing. At the point where each root attaches to the compressor casing, the root typically penetrates the casing and is retained by a boss formed on the outer side of the casing. Each vane requires a boss for its retention. In high solidity vane rows, i.e. vane rows with a relatively large number of vanes, the number of local bosses becomes so great that use of a continuous flange or ring with individual holes for each vane root becomes economical.
In order to improve engine efficiency at all operating conditions, it is known to supply actuating means for compressor stator vanes. Such actuating means typically attach to a root end of the vane and are effective for changing the vane pitch by rotating the vane about a vane axis. The actuation means is also responsible for limiting the amount of pitch variation as well as providing radial retention of each vane. In the event of a failure of the actuation means, a vane might spin on its axis creating vibration and other problems.